Functional Crown Architecture of Five Temperate Broadleaf Tree Species: Vertical Gradients in Leaf Morphology, Leaf Angle, and Leaf Area Density

Marc Hagemeier,Christoph Leuschner

doi:10.3390/f10030265

Abstract

The morphology, inclination, and spatial distribution of leaves in different parts of tree crowns are important determinants of the radiation, momentum, and gas exchange between the canopy and the atmosphere. However, it is not well known how these foliage-related traits vary among species differing in successional status. We measured leaf size, leaf mass area (LMA), leaf inclination (angle to the horizontal), leaf area density (LAD), total leaf area (leaf area index, LAI), and leaf area distribution across the crown in adult trees of five common, early to late-successional tree species (Betula pendula Roth, Quercus petraea (Matt.) Liebl., Carpinus betulus L., Tilia cordata Mill., and Fagus sylvatica L.) using different canopy access techniques and the harvest of foliated trees (29 trees in total). Leaf size increased continuously with crown depth in B. pendula and T. cordata but peaked at mid-crown in Q. petraea, C. betulus, and F. sylvatica to decrease toward the shade crown. By contrast, LMA and leaf angle decreased continuously with crown depth in all species, but the pattern of vertical change varied. The mid/late- and late-successional species had higher LAI, lower shade-leaf LMA, lower leaf angles (shade and sun crown), and higher LAD in the uppermost sun crown in comparison to early successional B. pendula. We assume that the most peripheral sun leaf layer is partly acting as a shield against excess radiation, with foliage properties depending on the structure of the shade crown. We conclude that the vertical change in leaf morphology, inclination, and spatial distribution in tree crowns is highly species specific, with partial dependence on the species’ position in succession.

Highlights

The size and shape of leaves and their three-dimensional position in crown space determine the exchange of radiation, gases, sensible heat, and momentum between forest canopies and the atmosphere
Area size increased linearly from the upper sun crown to the lowermost shade crown in Betula and Tilia, Our investigation of 22–26-m-tall adult trees in the upper canopy showed that mean leaf lamina while it peaked at 0.5–0.6 relative canopy height in Quercus, Carpinus, and Fagus and decreased toward size increased linearly from the upper sun crown to the lowermost shade crown in Betula and Tilia, the shade crown again (Figure 1)
Earlyand and late-successional speciesgenus have in leafearly-successional angles being steepesttree in the uppermost sun decreasing with species have in common leaf angles being steepest in the uppermost sun crown crown depth, independently of species differences in leaf size

Summary

Introduction

The size and shape of leaves and their three-dimensional position in crown space determine the exchange of radiation, gases, sensible heat, and momentum between forest canopies and the atmosphere. The foliage of a tree is exposed to highly variable environmental conditions along the vertical crown axis, triggering different acclimation processes of sun and shade leaves to radiation intensity and evaporative demand [2]. In most broadleaf canopies that have been studied so far, leaf size increased and leaf angles became progressively more horizontal from the tree top toward lower crown strata [4,5,6], which is generally explained by the exponential decrease in light intensity. Steeper leaf angles increase interception when the sun is at low angles (in the morning and evening hours and early and late in the season), and they can decrease the load of potentially harmful heat and excess radiation [7,8]

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Discussion

Conclusion